CAD-CAM 切削工具損耗對鈦金屬植體支台上氧化鋯牙冠準確度的影響

Abstract

問題陳述：牙科陶瓷材料的電腦輔助設計製造是一個切削和研磨的過程，會伴隨著切削工具表面的磨耗和材料碎屑的產生。切削工具的壽命會受到切削機台的種類、材料的硬度和大小等因素的影響。然而，切削工具隨著重複使用所產生的磨損，以及這些損耗對人工植體氧化鋯牙冠型態準確度的影響，仍有許多未知之處需要進一步評估。 研究目的：探討切削工具隨重複使用而產生的磨損情況，以及這些損耗對電腦輔助設計製造的人工植體氧化鋯牙冠準確度的影響。 研究方法與材料：製作一個左下第一小臼齒模擬人工植體的模型。使用五軸切削機台 (Coritec 250i; imes-icore GmbH) 和直徑1.0毫米的切削工具來製作氧化鋯牙冠 (3M Lava Esthetic; 3M ESPE)。每支切削工具製作26個成品，共重複五次 (N = 130)。每完成一次加工後，對切削工具進行影像拍攝與後處理，計算最大刀側值。氧化鋯牙冠成品的準確度通過以下方法測量：(1) 迭代最近點算法 (iterative closest point algorithm)、(2) 成品邊緣密合度測試、(3) 成品內面密合度測試、(4) x光放射影像評估。測量結果使用皮爾森積動差相關係數 (Pearson correlation coefficient, r) 評估工具切削時間與準確度之間的關係，組間及組內差異性比較將使用克拉斯卡－瓦立斯檢定 (Kruskal-Wallis test) 進行評估，事後檢定 (post hoc test) 為杜納檢定 (Dunn's test)。顯著水準 (significance level, α) 設定為 0.05。 結果：切削深度為0.15毫米的最大刀側值相關係數為0.248，具低度正相關性，數值從680.0 ± 8.4微米增加至684.8 ± 10.5 微米。迭代最近點算法中，外側面方均根值的相關係數為0.534，具高度正相關性，數值從35.4 ± 1.1微米增加至39.8 ± 2.0微米；內側面的相關係數為0.801，具高度正相關性，數值從33.0 ± 1.9微米增加至41.6 ± 3.3微米。邊緣密合度中，頰側面水平差異的相關係數為0.717，具高度正相關性，數值從17.9 ± 7.6 微米增加至52.3 ± 7.2 微米；垂直差異的相關係數為0.063，無明顯相關性，數值從7.1 ± 3.8 微米變化至8.7 ± 4.8 微米。遠心側水平差異的相關係數為0.401，具中度正相關性，數值從8.3 ± 5.6 微米增加至19.8 ± 11.3 微米；垂直差異的相關係數為 -0.011，無明顯相關性，數值從8.2 ± 5.9微米變化至9.6 ± 5.4 微米。舌側面水平差異的相關係數為0.696，具高度正相關性，數值從6.3 ± 4.5微米增加至26.0 ± 7.0微米；垂直差異的相關係數為0.241，具低度正相關性，數值從9.1 ± 5.2 微米稍微增加至12.6 ± 6.0 微米。近心側水平差異的相關係數為0.421，具中度正相關性，數值從6.4 ± 5.4 微米增加至15.8 ± 8.8 微米；垂直差異的相關係數為0.211，具低度正相關性，數值從8.6 ± 5.1 微米稍微增加至12.6 ± 7.0 微米。內面密合度中，薄膜厚度的相關係數為0.465，具中度正相關性，數值從24.6 ± 4.7 微米增加至32.4 ± 6.1微米。 結論：隨著不鏽鋼碳化鎢切削工具在切削氧化鋯的使用時間增加，工具的磨損顯著，對氧化鋯牙冠的加工型態準確度產生明顯影響。具體來說，外側面的加工正確度在切削工具使用約20% 後明顯變差，而內側面則在使用40% 後變差更為明顯。在水平方向上，邊緣密合度顯示出不同區域的變化，尤其是頰側面在使用切削工具20% 後密合度顯著變差；然而，在垂直方向上則沒有觀察到顯著的變化。在內面密合度方面，雖然在切削工具使用80% 後密合度有明顯變差，但測量結果仍在臨床上可接受的範圍內。

Statement of problem. The computer-aided design and manufacturing (CAD-CAM) of dental ceramic materials is a cutting and grinding process that involves wear on the cutting tool surfaces and the generation of material debris. The lifespan of the cutting tools is influenced by factors such as the type of milling machine, the hardness and size of the material. However, the wear of cutting tools with repeated use and the impact of this wear on the accuracy of zirconia crowns for dental implants still require further evaluation. Purpose. Investigate the wear of cutting tools with repeated use and the impact of this wear on the accuracy of zirconia crowns for dental implants manufactured using computer-aided design and manufacturing. Material and methods. A model simulating a mandibular left first premolar implant was created. A five-axis milling machine (Coritec 250i; imes-icore GmbH) and a 1.0 mm diameter cutting tool were used to fabricate zirconia crowns (3M Lava Esthetic; 3M ESPE). Each cutting tool could produce 26 finished products, and the process was repeated five times (N = 130). After each batch, the cutting tool was imaged and processed to calculate the maximum flank wear value. The accuracy of the zirconia crowns was measured through the following methods: (1) iterative closest point algorithm, (2) marginal fit test, (3) internal fit test, (4) x-ray radiographic image evaluation. The measurement results were evaluated for the relationship between tool cutting time and accuracy using the Pearson correlation coefficient (r). Differences between and within groups were assessed using the Kruskal-Wallis test, with Dunn's test as the post hoc test. The significance level (α) was set at 0.05. Results. The correlation coefficient for the maximum cutting width at a cutting depth of 0.15 mm was 0.248, indicating a low positive correlation, with values increasing from 680.0 ± 8.4 µm to 684.8 ± 10.5 µm. In the iterative closest point algorithm, the correlation coefficient for the root mean square value of the outer surface was 0.534, indicating a high positive correlation, with values increasing from 35.4 ± 1.1 µm to 39.8 ± 2.0 µm; the correlation coefficient for the inner surface was 0.801, indicating a high positive correlation, with values increasing from 33.0 ± 1.9 µm to 41.6 ± 3.3 µm. In the marginal fit test, the correlation coefficient for the horizontal discrepancy of the buccal surface was 0.716, indicating a high positive correlation, with values increasing from 17.9 ± 7.6 µm to 52.3 ± 7.2 µm; the correlation coefficient for the vertical discrepancy was 0.063, showing no significant correlation, with values changing from 7.1 ± 3.8 µm to 8.7 ± 4.8 µm. The correlation coefficient for the horizontal discrepancy of the distal surface was 0.401, indicating a moderate positive correlation, with values increasing from 8.3 ± 5.6 µm to 19.8 ± 11.3 µm; the correlation coefficient for the vertical discrepancy was -0.011, showing no significant correlation, with values changing from 8.2 ± 5.9 µm to 9.6 ± 5.4 µm. The correlation coefficient for the horizontal discrepancy of the lingual surface was 0.696, indicating a high positive correlation, with values increasing from 6.3 ± 4.5 µm to 26.0 ± 7.0 µm; the correlation coefficient for the vertical discrepancy was 0.241, indicating a low positive correlation, with values slightly increasing from 9.1 ± 5.2 µm to 12.6 ± 6.0 µm. The correlation coefficient for the horizontal discrepancy of the mesial surface was 0.421, indicating a moderate positive correlation, with values increasing from 6.4 ± 5.4 µm to 15.8 ± 8.8 µm; the correlation coefficient for the vertical discrepancy was 0.211, indicating a low positive correlation, with values slightly increasing from 8.6 ± 5.1 µm to 12.6 ± 7.0 µm. In the internal fit test, the correlation coefficient for the film thickness was 0.465, indicating a moderate positive correlation, with values increasing from 24.6 ± 4.7 µm to 32.4 ± 6.1 µm. Conclusion. With increased usage time of stainless steel tungsten carbide cutting tools in milling zirconia, significant tool wear occurs, markedly affecting the dimensional accuracy of zirconia crowns. Specifically, the trueness on the external surface significantly deteriorates after approximately 20% of tool usage, while the deterioration on the internal surface becomes more pronounced after 40% of usage. In the horizontal direction, variations in the marginal fit across different areas are evident, particularly the buccal surface, where the fit significantly worsens after 20% of tool use; however, no significant changes are observed in the vertical direction. Regarding the internal fit, although there is a noticeable decline after 80% of tool usage, the measurement results still remain within clinically acceptable limits.